In the title compound, C(13)H(17)NO(2)S, the thia-zolidine-1,4-dione ring adopts an envelope conformation with the S atom lying 0.631 (4) Å out of the plane formed by the other four ring atoms; the phenyl ring is almost perpendicular [88.74 (8)°] with respect to the ring C-C-N-C atoms and the butyl chain is in a fully extended conformation. In the crystal, a supra-molecular two-dimensional arrangement arises from weak inter-molecular C-H⋯O inter-actions.